#3787 Update public OpenTelemetry manual for remote waterfalls and execution metrics (#3786)

Documentation follow-up to https://swamp-club.com/lab/3786. Implementation is in progress; align publication with the final shipped contract. Update the public OpenTelemetry reference and how-to to cover: native serve → worker/runner → serve trace parentage across dispatch, query RPC and HTTP data writes; old-peer/invalid-carrier fallback; separate cold provisioning context (TRACEPARENT/TRACESTATE) and linked warm-worker lifecycle; explicit OTEL_METRICS_EXPORTER=otlp opt-in, metrics-specific endpoint/header precedence, histogram units/buckets, cumulative resets and service.instance.id; bounded operation/outcome dimensions and in-flight/oldest-age metrics; collector acknowledgment versus downstream delivery, export loss, sampling and uncovered/clock-uncertain time; committed writes versus transport receipt/ACK and unsupported reconciliation; webhook receipt and replay links. Source contract: design/enablers/remote-execution-telemetry.md in swamp. Include standard-viewer cold/warm examples and outcome-separated fixed-window benchmark interpretation, without claiming achieved 99% end-to-end phase coverage. The user is handling UAT acceptance manually; this issue is for the public manual only.